Retinol Binding Protein-4 Levels and Non-alcoholic Fatty Liver Disease: A community-based cross-sectional study

Cohort Profile: Guangzhou Nutrition and Health Study (GNHS): A Population-based Multi-omics Study

BACKGROUND

The Guangzhou Nutrition and Health Study (GNHS) aims to assess the determinants of metabolic disease in nutritional aspects, as well as other environmental and genetic factors, and explore possible biomarkers and mechanisms with multi-omics integration.

METHODS

The population-based sample of adults in Guangzhou, China (baseline: 40-83 years old; n = 5,118) was followed up about every 3 years. All are tracked via on-site follow-up and health information systems. We assessed detailed information on lifestyle factors, physical activities, dietary assessments, psychological health, cognitive function, body measurements, and muscle function. Instrument tests included dual-energy X-ray absorptiometry scanning, carotid artery and liver ultrasonography evaluations, vascular endothelial function evaluation, upper-abdomen and brain magnetic resonance imaging, and 14-day real-time continuous glucose monitoring tests. We also measured multi-omics, including host genome-wide genotyping, serum metabolome and proteome, gut microbiome (16S rRNA sequencing, metagenome, and internal transcribed spacer 2 sequencing), and fecal metabolome and proteome.

RESULTS

The baseline surveys were conducted from 2008 to 2015. Now, we have completed 3 waves. The 3rd and 4th follow-ups have started but have yet to end. A total of 5,118 participants aged 40-83 took part in the study. The median age at baseline was approximately 59.0 years and the proportion of female participants was about 69.4%. Among all the participants, 3,628 (71%) completed at least one on-site follow-up, with a median duration of 9.48 years.

CONCLUSION

The cohort will provide data that will be influential in establishing the role of nutrition in metabolic diseases with multi-omics.

Supplementation of Micro- and Macronutrients-A Role of Nutritional Status in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a condition in which the pathological cumulation of fat with coexisting inflammation and damage of hepatic cells leads to progressive dysfunctions of the liver. Except for the commonly well-known major causes of NAFLD such as obesity, dyslipidemia, insulin resistance, or diabetes, an unbalanced diet and imbalanced nutritional status should also be taken into consideration. In this narrative review, we summarized the current knowledge regarding the micro- and macronutrient status of patients suffering from NAFLD considering various diets and supplementation of chosen supplements. We aimed to summarize the knowledge indicating which nutritional impairments may be associated with the onset and progression of NAFLD at the same time evaluating the potential therapy targets that could facilitate the healing process. Except for the above-mentioned objectives, one of the most important aspects of this review was to highlight the possible strategies for taking care of NAFLD patients taking into account the challenges and opportunities associated with the micronutrient status of the patients. The current research indicates that a supplementation of chosen vitamins (e.g., vitamin A, B complex, C, or D) as well as chosen elements such as zinc may alleviate the symptoms of NAFLD. However, there is still a lack of sufficient data regarding healthy ranges of dosages; thus, further research is of high importance in this matter.

Influence of Adipokines on Metabolic Dysfunction and Aging

Currently, 30% of the global population is overweight or obese, with projections from the World Obesity Federation suggesting that this figure will surpass 50% by 2035. Adipose tissue dysfunction, a primary characteristic of obesity, is closely associated with an increased risk of metabolic abnormalities, such as hypertension, hyperglycemia, and dyslipidemia, collectively termed metabolic syndrome. In particular, visceral fat accretion is considered as a hallmark of aging and is strongly linked to higher mortality rates in humans. Adipokines, bioactive peptides secreted by adipose tissue, play crucial roles in regulating appetite, satiety, adiposity, and metabolic balance, thereby rendering them key players in alleviating metabolic diseases and potentially extending health span. In this review, we elucidated the role of adipokines in the development of obesity and related metabolic disorders while also exploring the potential of certain adipokines as candidates for longevity interventions.

PFOS-elicited metabolic perturbation in liver and fatty acid metabolites in testis of adult mice

Introduction

Multiple factors can contribute to sub-fecundity, including genetics, lifestyle, and environmental contaminants. PFASs are characterized as "forever chemicals" due to their ubiquitous contamination and their persistence in the environment, wildlife, and humans. Numerous studies have demonstrated that PFAS exposure adversely affects multiple bodily functions, including liver metabolism and gonadal function. It is unclear, however, how the disruption of hepatic fatty acid metabolism affects testicular function.

Methods

In this study, male mice were administered 0.3 and 3 μg/g body weight of PFOS for 21 days.

Results

Our data showed that PFOS exposure caused hepatic steatosis, as evidenced by significant increases in triglyceride levels, expression of ATP-citrate lyase, and fatty acid synthase, as well as fasting insulin levels. PFOS perturbed the expression levels of hepatokines, of which fibroblast growth factor-21 (Fgf-21), leukocyte cell-derived chemotaxin-2 (Lect-2), and retinol-binding protein-4 (Rbp-4) were significantly reduced, whereas angiopoietin-like 4 (Angptl4) was noticeably increased. While Rbp-4 and Fgf-21 are known to contribute to spermatogenesis and testosterone synthesis. In PFOS-exposed groups, testicular ATP, and testosterone decreased significantly with a significant increase in the expression of peroxisome proliferator-activated receptor-coactivator 1α. Mass spectrophotometry imaging revealed the localization of PFOS in testes, along with significant increases in fatty acid metabolites. These included arachidonic acid, dihomo-α-linolenic acid, dihomo-γ-linolenic acid, oxidized ceramide, diacylglycerol, phosphatidylcholine, and phosphatidylethanolamine, which are associated with inflammation and post-testicular causes of infertility.

Discussion

This study revealed potential links between PFOS-elicited changes in hepatic metabolism and their impacts on testicular biology. This study provides insights into alternative targets elicited by PFOS that can be used to develop diagnostic and therapeutic strategies for improving testicular dysfunction.

Emerging Links between Nonalcoholic Fatty Liver Disease and Neurodegeneration

The association between liver and brain health has gained attention as biomarkers of liver function have been revealed to predict neurodegeneration. The liver is a central regulator in metabolic homeostasis. However, in nonalcoholic fatty liver disease (NAFLD), homeostasis is disrupted which can result in extrahepatic organ pathologies. Emerging literature provides insight into the mechanisms behind the liver-brain health axis. These include the increased production of liver-derived factors that promote insulin resistance and loss of neuroprotective factors under conditions of NAFLD that increase insulin resistance in the central nervous system. In addition, elevated proinflammatory cytokines linked to NAFLD negatively impact the blood-brain barrier and increase neuroinflammation. Furthermore, exacerbated dyslipidemia associated with NAFLD and hepatic dysfunction can promote altered brain bioenergetics and oxidative stress. In this review, we summarize the current knowledge of the crosstalk between liver and brain as it relates to the pathophysiology between NAFLD and neurodegeneration, with an emphasis on Alzheimer's disease. We also highlight knowledge gaps and future areas for investigation to strengthen the potential link between NAFLD and neurodegeneration.

The relationship between NAFLD and retinol-binding protein 4 - an updated systematic review and meta-analysis

PURPOSE

Retinol-binding protein 4 (RBP4) has been considered to be related to metabolic related diseases, such as hyperuricemia, obesity, and diabetes mellitus. However, whether nonalcoholic fatty liver disease (NAFLD) is related to RBP4 is unclear. Previous studies on the relationship between NAFLD and RBP4 levels have yielded inconsistent results. Hence, this meta-analysis was aimed to clarify whether circulating RBP4 levels are in relation to the risk of NAFLD.

METHODS

A meta-analysis was performed by applying observational studies to evaluate circulating RBP4 levels and NAFLD. Eligible studies published up to September 23, 2022, were searched in Embase, PubMed, and Cochrane databases.

RESULTS

In this study, 17 cross-sectional studies involving 8423 participants were included. Results from a random effects model showed that circulating RBP4 levels were higher in NAFLD patients than non-NAFLD (standardized mean difference (SMD) 0.28; 95% confidence intervals (CI): 0.11-0.46, I²: 89.8%). This association was confirmed in the Yellow race. However, no significant association was noted in the Caucasian race. After excluding the morbidly obese Population from the weight loss study (n = 2), the results of the comparison remained largely unchanged (SMD 0.28; 95% CI: 0.10-0.47, I²: 90.8%). Remarkable publication bias was not found. Although considerable heterogeneity was observed among the studies, no potential sources of heterogeneity were found in the subgroup analysis. Diagnostic methods for NAFLD were determined to be a potential source of statistical heterogeneity in meta-regression.

CONCLUSION

The findings provide evidence that NAFLD patients exhibit higher levels of circulating RBP4 compared with controls, but high heterogeneity was observed. Thus, a high RBP4 level is probably a potential risk factor for NAFLD. To confirm the causal link between NAFLD and RBP4 level of causality, further prospective cohort studies are needed.

2019 Global NAFLD Prevalence: A Systematic Review and Meta-analysis

BACKGROUND & AIMS

The increasing rates of obesity and type 2 diabetes mellitus may lead to increased prevalence of nonalcoholic fatty liver disease (NAFLD). We aimed to determine the current and recent trends on the global and regional prevalence of NAFLD.

METHODS

Systematic search from inception to March 26, 2020 was performed without language restrictions. Two authors independently performed screening and data extraction. We performed meta-regression to determine trends in NAFLD prevalence.

RESULTS

We identified 17,244 articles from literature search and included 245 eligible studies involving 5,399,254 individuals. The pooled global prevalence of NAFLD was 29.8% (95% confidence interval [CI], 28.6%-31.1%); of these, 82.5% of included articles used ultrasound to diagnose NAFLD, with prevalence of 30.6% (95% CI, 29.2%-32.0%). South America (3 studies, 5716 individuals) and North America (4 studies, 18,236 individuals) had the highest NAFLD prevalence at 35.7% (95% CI, 34.0%-37.5%) and 35.3% (95% CI, 25.4%-45.9%), respectively. From 1991 to 2019, trend analysis showed NAFLD increased from 21.9% to 37.3% (yearly increase of 0.7%, P < .0001), with South America showing the most rapid change of 2.7% per year, followed by Europe at 1.1%.

CONCLUSIONS

Despite regional variation, the global prevalence of NAFLD is increasing overall. Policy makers must work toward reversing the current trends by increasing awareness of NAFLD and promoting healthy lifestyle environments.

NADPH Oxidases Connecting Fatty Liver Disease, Insulin Resistance and Type 2 Diabetes: Current Knowledge and Therapeutic Outlook

Nonalcoholic fatty liver disease (NAFLD), characterized by ectopic fat accumulation in hepatocytes, is closely linked to insulin resistance and is the most frequent complication of type 2 diabetes mellitus (T2DM). One of the features connecting NAFLD, insulin resistance and T2DM is cellular oxidative stress. Oxidative stress refers to a redox imbalance due to an inequity between the capacity of production and the elimination of reactive oxygen species (ROS). One of the major cellular ROS sources is NADPH oxidase enzymes (NOX-es). In physiological conditions, NOX-es produce ROS purposefully in a timely and spatially regulated manner and are crucial regulators of various cellular events linked to metabolism, receptor signal transmission, proliferation and apoptosis. In contrast, dysregulated NOX-derived ROS production is related to the onset of diverse pathologies. This review provides a synopsis of current knowledge concerning NOX enzymes as connective elements between NAFLD, insulin resistance and T2DM and weighs their potential relevance as pharmacological targets to alleviate fatty liver disease.

Non-alcoholic fatty liver disease: a multi-system disease influenced by ageing and sex, and affected by adipose tissue and intestinal function

In recent years, a wealth of factors are associated with increased risk of developing non-alcoholic fatty liver disease (NAFLD) and NAFLD is now thought to increase the risk of multiple extra-hepatic diseases. The aim of this review is first to focus on the role of ageing and sex as key, poorly understood risk factors in the development and progression of NAFLD. Secondly, we aim to discuss the roles of white adipose tissue (WAT) and intestinal dysfunction, as producers of extra-hepatic factors known to further contribute to the pathogenesis of NAFLD. Finally, we aim to summarise the role of NAFLD as a multi-system disease affecting other organ systems beyond the liver. Both increased age and male sex increase the risk of NAFLD and this may be partly driven by alterations in the distribution and function of WAT. Similarly, changes in gut microbiota composition and intestinal function with ageing and chronic overnutrition are likely to contribute to the development of NAFLD both directly (i.e. by affecting hepatic function) and indirectly via exacerbating WAT dysfunction. Consequently, the presence of NAFLD significantly increases the risk of various extra-hepatic diseases including CVD, type 2 diabetes mellitus, chronic kidney disease and certain extra-hepatic cancers. Thus changes in WAT and intestinal function with ageing and chronic overnutrition contribute to the development of NAFLD – a multi-system disease that subsequently contributes to the development of other chronic cardiometabolic diseases.

The association between retinol-binding protein 4 and prediabetes in obese patients with nonalcoholic fatty liver disease

CONTEXT

Retinol-binding protein 4 (RBP4) is associated with visceral fat and insulin resistance (IR) in obesity, type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD), but some of these data remain controversial.

OBJECTIVE

This study evaluated the relationship between serum RBP4 levels and prediabetes in obese patients with NAFLD.

METHODS

A total of 79 obese NAFLD patients without (n = 41) and with prediabetes (n = 38) were included. Serum RBP4 was measured using ELISA method.

RESULTS

Higher RBP4 serum levels were observed in patients with prediabetes, metabolic syndrome (MetS), or dyslipidaemia. There was correlation between RBP4 levels and visceral adiposity index (VAI), glucose, insulin, HOMA-IR, and Quicki index. RBP4 ≥ 61 mcg/ml have about 3.5-fold higher risk of prediabetes (OR 3.544, 95% CI 1.385-9.072, p=.008), and RBP4 ≥ 55 mcg/ml increased the risk for MetS approximately 3.1 times.

CONCLUSIONS

RBP4 is associated with increased risk for prediabetes and MetS in obese patients with NAFLD.

Serum Retinol-Binding Protein Levels Are Associated with Nonalcoholic Fatty Liver Disease in Chinese Patients with Type 2 Diabetes Mellitus: A Real-World Study

BACKGROUND

The association of serum retinol-binding protein (RBP) levels with nonalcoholic fatty liver disease (NAFLD) remains controversial. Furthermore, few studies have investigated their relationship in type 2 diabetes mellitus (T2DM) patients. Therefore, the aim of the present study was to explore the association between serum RBP levels and NAFLD in Chinese inpatients with T2DM.

METHODS

This cross-sectional, real-world study included 2,263 Chinese T2DM inpatients. NAFLD was diagnosed by abdominal ultrasonography. The subjects were divided into four groups based on RBP quartiles, and clinical characteristics were compared among the four groups. The associations of both RBP levels and quartiles with the presence of NAFLD were also analyzed.

RESULTS

After adjustment for sex, age, and diabetes duration, there was a significant increase in the prevalence of NAFLD from the lowest to the highest RBP quartiles (30.4%, 40.0%, 42.4%, and 44.7% for the first, second, third, and fourth quartiles, respectively, P<0.001 for trend). Fully adjusted multiple logistic regression analysis revealed that both increased RBP levels (odds ratio, 1.155; 95% confidence interval, 1.012 to 1.318; P=0.033) and quartiles (P=0.014 for trend) were independently associated with the presence of NAFLD in T2DM patients.

CONCLUSION

Increased serum RBP levels were independently associated with the presence of NAFLD in Chinese T2DM inpatients. Serum RBP levels may be used as one of the indicators to assess the risk of NAFLD in T2DM patients.

Associaton of Retinol Binding Protein 4 (RBP4) Levels With Hyperuricemia: A Cross-Sectional Study in a Chinese Population

BACKGROUND

There are few studies on predictive biomarkers for hyperuricemia, and the predictive value of these biomarkers tends to be poor. Additionally, no reports have described the predictive value of retinol binding protein 4 (RBP4) for hyperuricemia.

PURPOSE

This study was performed to evaluate the value of RBP4 for predicting the risk of hyperuricemia in a general population, determine whether RBP4 could be used alone or in combination with other factors to predict the risk of hyperuricemia in the general population, and establish an optimum predictive model.

METHODS

We conducted a population-based cross-sectional survey in 2018, involving a questionnaire, physical examination, and laboratory testing. We enrolled 2303 individuals by stratified random sampling, and 2075 were included in the data analysis after applying the eligibility criteria.

RESULTS

Serum RBP4 level had a highly significant association with hyperuricemia (P<0.001). After adjusting for potential confounders, logistic regression indicated that the risk of hyperuricemia was highest in the highest RBP4 quartile (odds ratio: 7.9, 95% confidence interval [CI]: 4.18-14.84, compared to the lowest quartile). The area under the receiver operating characteristic (ROC) curve (AUC) for RBP4 was 0.749 (95% CI: 0.725-0.774, P<0.001), which was higher than that for all the other predictors assessed. The optimum model for predicting hyperuricemia in the general population consisted of RBP4, sex (male), body mass index, serum creatinine, high-sensitivity C-reactive protein, fasting blood glucose, insulin, and alcohol consumption. The AUC was 0.804 (95% CI: 0.782-0.826, P<0.001).

CONCLUSIONS

RBP4 is strongly associated with hyperuricemia, and its predictive value was higher than that of traditional predictors.

Optimised expression and purification of RBP4 and preparation of anti-RBP4 monoclonal antibody

The expression level of retinol-binding protein 4 (RBP4) protein is closely related to liver damage and plays an important role in the diagnosis and prognosis of cancer. However, the preparation of anti-RBP4 mAb or exploration on the application of anti-RBP4 mAb has not been reported thus far. In the present study, we constructed a pET30a-RBP4 recombinant vector, used E. coli BL21 (DE3) as the vector to express the RBP4 recombinant protein and prepared anti-RBP4 mAb using hybridoma technology. We performed immunohistochemical analysis on hepatocellular carcinoma (HCC) and adjacent tissues by using this anti-RBP4 mAb. In addition to the high-purity RBP4 recombinant protein, we successfully developed the anti-RBP4 mAb with high affinity and specificity; it binds to natural RBP4 protein and is suitable for immunohistochemical analysis.

Beneficial Effects of Tamarind Trypsin Inhibitor in Chitosan-Whey Protein Nanoparticles on Hepatic Injury Induced High Glycemic Index Diet: A Preclinical Study

Several studies have sought new therapies for obesity and liver diseases. This study investigated the effect of the trypsin inhibitor isolated from tamarind seeds (TTI), nanoencapsulated in chitosan and whey protein isolate (ECW), on the liver health status of the Wistar rats fed with a high glycemic index (HGLI) diet. The nanoformulations without TTI (CW) and ECW were obtained by nanoprecipitation technique, physically and chemically characterized, and then administered to the animals. The adult male Wistar rats (n = 20) were allocated to four groups: HGLI diet + water; standard diet + water; HGLI diet + ECW (12.5 mg/kg); and HGLI diet + CW (10.0 mg/kg), 1 mL per gagave, for ten days. They were evaluated using biochemical and hematological parameters, Fibrosis-4 Index for Liver Fibrosis (FIB-4), AST to Platelet Ratio Index (APRI) scores, and liver morphology. Both nanoparticles presented spherical shape, smooth surface, and nanometric size [120.7 nm (ECW) and 136.4 nm (CW)]. In animals, ECW reduced (p < 0.05) blood glucose (17%), glutamic oxalacetic transaminase (39%), and alkaline phosphatase (24%). Besides, ECW reduced (p < 0.05) APRI and FIB-4 scores and presented a better aspect of hepatic morphology. ECW promoted benefits over a liver injury caused by the HGLI diet.

The effect of combined exercises on the plasma levels of retinol-binding protein 4 and its relationship with insulin resistance and hepatic fat content in postmenopausal women with nonalcoholic fatty liver disease

BACKGROUND

Evidence suggests increased serum levels of retinol-binding protein 4 (RBP4) in postmenopausal women with nonalcoholic fatty liver disease (NAFLD). This study investigated the effect of combined exercises on the plasma levels of RBP4 and its relationship with insulin resistance and hepatic fat content in these women.

METHODS

This quasi-experimental study randomly assigned 24 women with fatty liver and a mean age of 56.18±4.58 years to an experimental group and a control group. The experimental group participated in ten-week incremental endurance-resistance training as combined exercises three sessions a week. Fatty liver was diagnosed with ultrasound, RBP4 levels were measured and insulin resistance was determined using the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Between-group data were analyzed using ANCOVA, within-group data using the dependent t-test and Wilcoxon test and relationships between RBP4 and variables using Spearman and Pearson correlation coefficients.

RESULTS

Ten weeks of combined exercises significantly decreased RBP4 levels (P=0.000), HOMA-IR (P=0.011) and hepatic fat levels (P=0.000) in the experimental group compared to in the controls. The posttest showed significant correlations between RBP4 levels and hepatic fat levels (P=0.002) and no correlations between RBP4 levels and insulin resistance (P=0.116).

CONCLUSIONS

Combined exercises significantly reduced serum levels of RBP4 in postmenopausal women with fatty liver. RBP4 was not related to insulin resistance and effects of RBP4 on hepatic fat regulation were independent of the effects of insulin resistance.

Influence of irisin on diet-induced metabolic syndrome in experimental rat model

OBJECTIVE

To evaluate the influence of irisin on the experimental paradigm of non-alcoholic fatty liver (NAFL) as a part of MetS cluster.

METHODS

Forty male albino rats were divided into four groups; normal control, standard diet + irisin, high carbohydrate and fat diet (HCHF), and HCHF + irisin. After the experimental period, levels of fasting blood sugar (FBS), insulin, lipid profile, kidney functions, salusin-alpha (Sal-α), adropin, and retinol-binding protein-4 (RBP-4) were evaluated. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1α) expression in skeletal muscle was evaluated by quantitative real-time PCR. Aorta, liver, pancreas, and skeletal muscle tissue samples were prepared for histopathological examination.

RESULTS

Rats administrated HCHF showed elevated levels of FBS, lipid profile, kidney functions, RBP-4, and downregulation of PGC-1α expression along with a decline in levels of insulin, Sal-α, and adropin while administration of irisin significantly attenuated these levels.

CONCLUSIONS

Irisin as based therapy could emerge as a new line of treatment against MetS and its related diseases.

Serum proteome assessment in nonalcoholic fatty liver disease in children: a preliminary study

OBJECTIVES

Nonalcoholic fatty disease (NAFLD) affects 3-10% of the pediatric population, making it the most common chronic liver disease among children. The aim of the study is to identify potential biomarkers enabling the diagnosis of NAFLD and monitoring the course of the disease.

METHODS

Proteome analysis was performed in a group of 30 patients (19 boys and 11 girls) in total, of whom 16 children had previously diagnosed NAFLD based on the abdominal ultrasound after excluding other diseases of this organ.

RESULTS

A total of 297 proteins have been identified. Thirty-seven proteins (responsible for inflammation, stress response, and regulation of this process) differentiating both experimental groups were identified. Up-regulated proteins included afamin, retinol-binding protein-4, complement components, and hemopexin; while serum protease inhibitors, clusterin, immunoglobulin chains, and vitamin D binding protein were found in the down-regulated group. The correlation between selected proteins and indicators of noninvasive assessment of liver fibrosis (APRI, FIB-4) as well as differences between the serum proteome of patients with normal weight, overweight, and obesity were also assessed.

CONCLUSION

The plasma protein profile is significantly altered in nonalcoholic liver disease in children and may prove to be a valuable source of biomarkers to evaluate the extent of liver disease.

Adipocytokines in Steatotic Liver Surgery/Transplantation

Because of the shortage of liver grafts available for transplantation, the restrictions on graft quality have been relaxed, and marginal grafts, such as steatotic livers, are now accepted. However, this policy change has not solved the problem, because steatotic liver grafts tolerate ischemia-reperfusion (I/R) injury poorly. Adipocytokines differentially modulate steatosis, inflammation, and fibrosis and are broadly present in hepatic resections and transplants. The potential use of adipocytokines as biomarkers of the severity of steatosis and liver damage to aid the identification of high-risk steatotic liver donors and to evaluate hepatic injury in the postoperative period are discussed. The hope of finding new therapeutic strategies aimed specifically at protecting steatotic livers undergoing surgery is a strong impetus for identifying the mechanisms responsible for hepatic failure after major surgical intervention. Hence, the most recently described roles of adipocytokines in steatotic livers subject to I/R injury are discussed, the conflicting results in the literature are summarized, and reasons are offered as to why strategic pharmacologic control of adipocytokines has yet to yield clinical benefits. After this, the next steps needed to transfer basic knowledge about adipocytokines into clinical practice to protect marginal livers subject to I/R injury are presented. Recent strategies based on adipocytokine regulation, which have shown efficacy in various pathologies, and hold promise for hepatic resection and transplantation are also outlined.

Vitamin A signaling and homeostasis in obesity, diabetes, and metabolic disorders

Much evidence has accumulated in the literature over the last fifteen years that indicates vitamin A has a role in metabolic disease prevention and causation. This literature proposes that vitamin A can affect obesity development and the development of obesity-related diseases including insulin resistance, type 2 diabetes, hepatic steatosis and steatohepatitis, and cardiovascular disease. Retinoic acid, the transcriptionally active form of vitamin A, accounts for many of the reported associations. However, a number of proteins involved in vitamin A metabolism, including retinol-binding protein 4 (RBP4) and aldehyde dehydrogenase 1A1 (ALDH1A1, alternatively known as retinaldehyde dehydrogenase 1 or RALDH1), have also been identified as being associated with metabolic disease. Some of the reported effects of these vitamin A-related proteins are proposed to be independent of their roles in assuring normal retinoic acid homeostasis. This review will consider both human observational data as well as published data from molecular studies undertaken in rodent models and in cells in culture. The primary focus of the review will be on the effects that vitamin A per se and proteins involved in vitamin A metabolism have on adipocytes, adipose tissue biology, and adipose-related disease, as well as on early stage liver disease, including non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH).

Update on the human and mouse lipocalin (LCN) gene family, including evidence the mouse Mup cluster is result of an "evolutionary bloom"

Lipocalins (LCNs) are members of a family of evolutionarily conserved genes present in all kingdoms of life. There are 19 LCN-like genes in the human genome, and 45 Lcn-like genes in the mouse genome, which include 22 major urinary protein (Mup) genes. The Mup genes, plus 29 of 30 Mup-ps pseudogenes, are all located together on chromosome (Chr) 4; evidence points to an “evolutionary bloom” that resulted in this Mup cluster in mouse, syntenic to the human Chr 9q32 locus at which a single MUPP pseudogene is located. LCNs play important roles in physiological processes by binding and transporting small hydrophobic molecules —such as steroid hormones, odorants, retinoids, and lipids—in plasma and other body fluids. LCNs are extensively used in clinical practice as biochemical markers. LCN-like proteins (18–40 kDa) have the characteristic eight β-strands creating a barrel structure that houses the binding-site; LCNs are synthesized in the liver as well as various secretory tissues. In rodents, MUPs are involved in communication of information in urine-derived scent marks, serving as signatures of individual identity, or as kairomones (to elicit fear behavior). MUPs also participate in regulation of glucose and lipid metabolism via a mechanism not well understood. Although much has been learned about LCNs and MUPs in recent years, more research is necessary to allow better understanding of their physiological functions, as well as their involvement in clinical disorders.

Ultrasound/Elastography techniques, lipidomic and blood markers compared to Magnetic Resonance Imaging in non-alcoholic fatty liver disease adults

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) may progress to steatohepatitis, cirrhosis and complicated hepatocellular carcinoma with defined differential symptoms and manifestations.

OBJECTIVE

To evaluate the fatty liver status by several validated approaches and to compare imaging techniques, lipidomic and routine blood markers with magnetic resonance imaging in adults subjects with non-alcoholic fatty liver disease.

MATERIALS AND METHODS

A total of 127 overweight/obese with NAFLD, were parallelly assessed by Magnetic Resonance Imaging (MRI), ultrasonography, transient elastography and a validated metabolomic designed test to diagnose NAFLD in this cross-sectional study. Body composition (DXA), hepatic related biochemical measurements as well as the Fatty Liver Index (FLI) were evaluated. This study was registered as FLiO: Fatty Liver in Obesity study; NCT03183193.

RESULTS

The subjects with more severe liver disease were found to have worse metabolic parameters. Positive associations between MRI with inflammatory and insulin biomarkers were found. A linear regression model including ALT, RBP4 and HOMA-IR was able to explain 40.9% of the variability in fat content by MRI. In ROC analyses a combination panel formed of ALT, HOMA-IR and RBP4 followed by ultrasonography, ALT and metabolomic test showed the major predictive ability (77.3%, 74.6%, 74.3% and 71.1%, respectively) for liver fat content.

CONCLUSIONS

A panel combination including routine blood markers linked to insulin resistance showed highest associations with MRI considered as a gold standard for determining liver fat content. This combination of tests can facilitate the diagnosis of early stages of non-alcoholic liver disease thereby avoiding other invasive and expensive methods.

Association between urine retinol-binding protein levels and nonalcoholic fatty liver disease: A cross-sectional study in Chinese population

OBJECTIVE

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been rapidly increased, becoming a public health problem worldwide. Our objective was to investigate the association between urine retinol-binding protein (RBP) and NAFLD in a Chinese population and develop a multivariate logistic regression model for NAFLD prediction.

METHODS

A total of 317 NAFLD patients and 391 healthy controls were enrolled in this cross-sectional study based on inclusion and exclusion criteria, from whom fasting urine and blood were collected for further study. Urine RBP level and other parameters were measured and compared between NAFLD subjects and controls.

RESULTS

Urine RBP levels (expressed by RBP/creatinine ratio) in NAFLD patients were significantly higher than controls (median 133.1 mg/g vs 110.7 mg/g; P < .001). Urine RBP/creatinine ratio was verified as an independent factor for NAFLD prediction after adjustment in multivariate logistic regression. The area under curve (AUC) of receiver operating characteristic (ROC) was 0.889 with the 95% confidence interval from 0.867 to 0.912.With a cutoff point of 0.215, the sensitivity and specificity of urine RBP/creatinine ratio in NAFLD prediction were 81.1% and 84.5%, respectively.

CONCLUSION

Our results demonstrated that urine RBP/creatinine ratio was an independent risk factor for NAFLD while the predictive model for NAFLD diagnosis is noninvasive with high sensitivity and specificity.

Circulating retinol binding protein 4 levels in nonalcoholic fatty liver disease: a systematic review and meta-analysis

Background

Retinol binding protein 4 (RBP4) is implicated in obesity, insulin resistance and type 2 diabetes mellitus that are closely associated with nonalcoholic fatty liver disease (NAFLD). However, recent investigations regarding circulating RBP4 levels in NAFLD are conflicting. This meta-analysis is to determine whether NAFLD, non-alcoholic steatohepatitis (NASH) and simple steatosis (SS) patients have altered RBP4 levels.

Methods

We performed a systematic search in PubMed, EMBASE and The Cochrane Library up until 18 March 2017, and 12 studies comprising a total of 4247 participants (2271 NAFLD patients and 1976 controls) were included in the meta-analysis.

Results

There were no significant differences of circulating RBP4 levels in the following comparisons: (1) NAFLD patients vs controls (standardized mean differences [SMD]: 0.08; 95% CI: −0.21, 0.38); (2) NASH patients vs controls (SMD: −0.49; 95% CI: −1.09, 0.12); (3) SS patients vs controls (SMD: −0.72; 95% CI: −1.64, 0.20) and (4) NASH vs SS patients (SMD: −0.04; 95% CI: −0.32, 0.24). The results remained essentially unchanged in the comparisons between NAFLD patients and controls after excluding single individual study or bariatric studies (n = 2). No significant publication bias was detected. However, there was significant heterogeneity among studies and the subgroup and meta-regression analyses did not find the potential sources.

Conclusions

Circulating RBP4 levels may not be associated with NAFLD. Further prospective cohort studies are required to confirm these findings.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0566-7) contains supplementary material, which is available to authorized users.